The ultimate goal of the project is to produce antitoxic sera of Pseudomonas aeruginosa that may be useful in the treatment of infections caused by this organisms. There are more than one serotype of the exotoxin of this species and only one, designated exotoxin A, is well characterized at present. In the next period we plan to screen a large number of strains of P. aeruginosa to find nonproteolytic strains that are good producers of exotoxins other than toxin A. Preliminary data indicate that there are at least two more serotypes of exotoxins produced by this species and we wish to find strains that will produce these toxins in high titers to facilitate concentration and purification. Once the toxins are purified we would like to see if we can convert them to toxoids in order to immunize men and animals for production of antitoxic sera. The present grant is also supporting an international effort to establish a serotyping schema of P. aeruginosa based on the heat stable somatic antigen. This is a project of the Subcommittee on Pseudomonadaceae of the International Committee on Systematic Bacteriology. An international panel of experts in this field have been organized for this purpose and through exchange of strains as well as antisera we have identified at least 16 distinct antigens that will form the basis of the further international serotypes. This effort will continue to arrive at a serotyping schema that would be used by microbiologists throughout the world.